1. Field of the Invention. This invention pertains to navigation, and more particularly to apparatus that facilitates aircraft navigation.
2. Description of the Prior Art. Numerous types of equipment have been developed to assist pilots navigate their aircraft. Hardware such as compasses, variable omni-directional radio range transmitters and receivers (VOR), non-directional beacon (NDB) radio transmitters and receivers, automatic direction finders (ADF), and distance measuring equipment (DME) are in widespread use. Aeronautic charts are commonly used. It is also known to correlate actual flying variables such as position, heading, and distance with aeronautic charts by means of relatively small hand held instruments. Examples of such instruments are disclosed in U.S. Pat. Nos. 2,736,096; 2,996,242; 3,059,339; 3,303,568; 3,690,009; 3,813,783; 3,855,706; 4,095,342; and Great Britain Pat. No. 381,613. U.S. Pat. No. 2,085,059 describes an instrument especially useful for navigating boats. Another instrument is marketed under the trademark Super Plotter by the Dorcliff Company of Placerville, Calif. The devices of most of the foregoing patents employ a compass rose having a central axis for locating over a desired point on an aeronautical chart, usually a point of departure or destination. Various combinations of arms are pivotable about the compass rose central axis. Indicia are usually inscribed on the compass rose and arms for displaying information representing navigational parameters.
The navigational instruments mentioned above are intended primarily for use by pilots of small airplanes. However, in such applications, the known instruments suffer several important disadvantages. Those disadvantages include the relatively rigid material from which the instruments are made. A common material is a clear plastic that, when considered alone, is relatively flexible. However, when used with a chart on the pilot's lap in a cramped cockpit of a small airplane, the material of the prior instruments acquires a rigidity that precludes easy handling and manipulation. Another handicap of prior instruments is that they lack convenient means for releasably attaching them to a chart. To be effective, such attachment and release must be done with one hand, leaving the other hand free for the pilot to control his airplane. Fasteners such as tacks and pins are mentioned in the prior art, but such fasteners are entirely impractical for use in a small aircraft. It is known to adhere instruments to a backing surface with individual pieces of adhesive tape, but that method is also unsatisfactory in flying situations, as it requires the use of two hands. Because of the lack of a suitable way to fasten existing navigational instruments to charts, it is very difficult and sometimes impossible for a pilot to manipulate the instruments with one hand. Similarly, it s virtually impossible for the pilot to manipulate two instruments on a chart so as to enable him to navigate by triangulation.
There is no equipment presently available that deals effectively with identifying on a chart an aircraft's position relative to NDB radio transmitters without requiring the pilot to perform mental arithmetic to deduce magnetic bearings to or from the NDB transmitter. Different shortcuts and methods are routinely taught to assist pilots to perform the required mental arithmetic, but no device or instrument has been developed that can both eliminate the mental mathematics and simultaneously show the pilot his location directly on a chart. Similarly, there is no equipment presently available that effectively identifies directly on a chart the effects of crosswind on the course of an aircraft flying directly to or from an NDB radio transmitter.
An additional shortcoming of known navigational aids is that they are designed for use by persons already skilled at navigation. On the other hand, students and others who are inexperienced in actual navigation are unable to successfully and reliably use the prior instruments to visualize their positions and headings. Such limited usefulness is partially caused by the lack of suitable teaching aids included among the prior navigational instruments, and partially by the inconvenient arrangement of the navigational indicia printed on prior instruments.
Thus, a need exists for a navigational instrument that is useful to experienced and student pilots under actual flight conditions.